Officials have said that gunmen have fired at a helicopter carrying voting material for today's election, killing an electoral worker.
The helicopter made a forced landing outside the eastern town of Benghazi.
The identity of the attackers is not known, but eastern Libya has been a focus of unrest by groups seeking greater regional autonomy.
The parliamentary poll is the first national vote since Col Muammar Gaddafi was toppled last year.
The news came as armed men closed at least three oil export terminals in the east in protest at the vote.
They are angry that the west of the country has been granted more seats in the new 200-member General National Congress than the oil-rich east.
The current system allocates 100 seats to the west, 60 to the east and 40 to the south.